[SignalOne] QRM, QRN.

Thu, 11 Dec 2003 16:08:11 +0100

Hi,

we have - besides strong medium wave broadcasters - very strong signals 
at 6.xxx and 7.1xx MHz and at higher frequencies. Those at 6 Mhz create 
sum products with medium wave signals and you hear them at 7.xxx Mhz as 
well as the 3rd order products from 7.1xx MHz directly. 7 MHz signals 
further add up to 14 and 21 MHz. These signals appear at levels of 10 
to 200 mV average each and sum up to more than several volts on a full 
size dipol without selective antenna tuner. Only very few radios manage 
to work without producing second order IM distortion like the TR-7, the 
KWM-380 or the new IC-7400, the real exception from far east. IM3 can 
only be conquered with a good mixer and the milspec is beyond critizism. 
Only the TR-7 equals the Milspec performance.

But - and nobody so far commented this point - there is a much worse 
characteristic of especially the Milspec. It has the worst sideband 
noise wrecked synthesizer I ever measured. Just take a strong clean 
signal from a xtal oszillator, feed it into the receiver and tune it 
aside the slopes of the filters. You will not manage to measure ultimate 
selectivity or filter shape factor due to extremely high sideband noise. 
This does not affect standard communication but heavy contest work 
and it is not audible, but a severe technical drawback. In my Milspec I
discovered a handmade A24 module, completely enclosed in a housing made
from pcb sheets - an original S/1-option! So esthetic aspects could be 
spoiled after a look inside the radio! I rebuilt and modified the original 
circuitry and mounted it in a milled case at the original position. 
Looks now better than original and meets at least my personal esthetic 
demands, hi. Although there was a lot of work to do on this radio I 
really love it and will not trade it away any more.

73 Uli, DK4SX

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of
[email protected]
Sent: Donnerstag, 11. Dezember 2003 13:42
To: [email protected]
Subject: [SignalOne] QRM, QRN.

I guess the problem in Europe is the proximity of the big SW broadcast
stations?  There are some stations that hammer into the East Coast of
the U.S. at, what, a couple volts at the antenna?  It seems that way.

The S-meter pegs on both the S/1 and my IC-720A.  Sometimes I wonder if
I couldn't light an LED off a 40 meter dipole.

Other than that, the problem at my QTH is an S-7 noise level, it's a
bzzzzzz across most of the HF bands, with peaks of shot noise every 40,
50 kHz.   

I bought a pocket SWL radio from www.countrycomm.com to use as a
"sweep" for the noise source.   It should be here later today.

I agree with the sentiment that the Signal/One's are nice to look at.
Not so much from the pure esthetics perspective but for what they
represent. The S/1 was intended to be the top radio just as the Alpha.  

>From what I can tell, both missed the mark.  It's like Heathkit gunning
for Collins.  The Heath SB-series had many advantages over Collins, the
500 kHz LMO, the wide range of accessories.  Some folks convert Heath
monitor scopes to the S-Line look.

Where Heath fell down was in the execution.  The SB front panel and the
LMO bezel look cheap.  Ten bucks more, a thicker front panel with
embossed sub panels, a little more attention to detail.  I have an
SB-313, if Heath had used a flip lid case and put an accessory crystal
bank in it like the 75S3C, they would have a killer SWL receiver.

If they had designed in space for synthesizer option, went after the
51J market.  If only. 

Frankly, some parts of the S/1 look homebrewed.  The mechanicals,
especially the shaft sticking out the back and the off-set universals
don't belong in a multi-thousand dollar (1970's price) product.

Don't get me started on the perf-metal RF shielding.  My Heathkit DX-60
has nicer looking perf-metal than the S/1.  

Explain why almost every knob on the CX7A is different from its
neighbor, why the knobs are "wobbly", and why the skirts are so thin?

Some knobs look like witches hats.  Signal/One needed an industrial
designer.

So there were trade-offs.  I understand that.  

But it is the top radio and a milestone in transceiver design.  If I
can get it working at 100%; might take a year but I have the time.

de ah6gi/4 

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